Sixteen (53.3%) patients (32 eyes) in the Demodex-negative group and 21 (70%) patients (42 eyes) in the Demodex-positive group had TBUT values less than 10 seconds. Eighteen (60%) patients (36 eyes) in the Demodex-negative group and 25 (83.3%) patients (50 eyes) in the Demodex-positive group had Schirmer scores less than 10 mm (Table 3). The 2 groups were not significantly different in dry eye findings (P=.25 and P=.29, respectively).
Comment
Inflammation in Rosacea
It is known that the density of nonfloral bacteria as well as D folliculorum and Demodex brevis increases in skin affected by rosacea compared to normal skin. Vascular dilation associated with rosacea that results from sunlight and heat causes increased capillary permeability and creates the ideal environment for the proliferation of D folliculorum. Demodex is thought to act as a vector for the activity of certain other microorganisms, particularly Bacillus oleronius, and thus initiates the inflammatory response associated with rosacea.9
One study reported that the inflammation associated with rosacea that was caused by Demodex and other environmental stimuli occurred through toll-like receptor 2 and various cytokines.10 It has been reported that the abnormal function of toll-like receptor 2 in the epidermis leads to the increased production of cathelicidin. Cathelicidin is an antimicrobial peptide with both vasoactive and proinflammatory activity and has been used as a basis to explain the pathogenesis of facial erythema, flushing, and telangiectasia in the context of rosacea.11,12 In addition, it has been reported that the increased secretion of proinflammatory cytokines such as IL-1 and gelatinase B in ocular rosacea leads to tearing film abnormalities that result from increased bacterial flora in the eyelids, which subsequently leads to decreased tear drainage and dry eyes.13 In addition, B oleronius isolated from a D folliculorum mite from patients with PPR produced proteins that induced an inflammatory immune response in 73% (16/22) of patients with rosacea.14
Ocular Findings in Rosacea Patients
In our study, PPR was found to be significantly associated with Demodex positivity compared to ETR and phymatous rosacea (P=.003). However, ocular inflammation findings such as blepharitis and meibomitis were not significantly different between Demodex-positive and Demodex-negative patients. Although the mean Schirmer score of Demodex-positive patients was lower than Demodex-negative patients, this difference was not statistically significant. We evaluated a TBUT of less than 10 seconds and a Schirmer score less than 10 mm as dry eye. Accordingly, the number of patients with dry eye was higher in the Demodex-positive group, but this difference was not statistically significant.
Chronic blepharitis, conjunctival inflammation, and meibomian gland dysfunction are among the most common findings of ocular rosacea.15,16 Patients with ocular rosacea commonly have dry eye and abnormal TBUT and Schirmer scores.17 In our study, we found that the fluorescein TBUT and Schirmer scores were more likely to be abnormal in the Demodex-positive group, but the difference between the 2 groups was not statistically significant.
It has been reported that proinflammatory cytokines due to a weakened immune system in rosacea patients were increased. The weakened immune system was further supported by the increased concentrations of proinflammatory cytokines such as IL-1 and matrix metalloproteinase 9 in these patients’ tears and the improvement of symptoms after the inhibition of these cytokines.11 Luo et al18 reported that Demodex inflammation causes dry eye, particularly with D brevis. Ayyildiz and Sezgin19 reported that Schirmer scores were significantly lower and that the Ocular Surface Disease Index had significantly increased in the Demodex-positive group compared to the Demodex-negative group (P=.001 for both). A Korean study reported that Demodex density was correlated with age, sex, and TBUT results, but there was no significant relationship between Demodex density and Schirmer scores.16
Sobolewska et al20 administered ivermectin cream 1% to 10 patients with cutaneous and ocular rosacea, but only to the forehead, chin, nose, cheeks, and regions close to the eyelids, and observed a significant improvement in blepharitis (P=.004). They stated that ivermectin, as applied only to the face, suppressed the proinflammatory cytokines associated with rosacea and showed anti-inflammatory effects by reducing Demodex mites.20Li et al21 demonstrated a strong correlation between ocular Demodex inflammation and serum reactivity to these bacterial proteins in patients with ocular rosacea, and they found that eyelid margin inflammation and facial rosacea correlated with reactivity to these proteins. These studies suggest a possible role for Demodex infestation and bacterial proteins in the etiology of rosacea.
Gonzalez-Hinojosa et al22 demonstrated that even though eyelash blepharitis was more common in PPR than ETR, there was no statistically significant association between rosacea and Demodex blepharitis. In our study, we found a significant correlation between PPR and Demodex positivity. Also, meibomian gland dysfunction was more common in the Demodex-positive group; however, this result was not statistically significant. One study compared patients with primary demodicosis and patients with rosacea with Demodex-induced blepharitis to healthy controls and found that patients with primary demodicosis and patients with rosacea did not have significantly different ocular findings.23 In contrast, Forton and De Maertelaer24 reported that patients with PPR had significantly more severe ocular manifestations compared with patients with demodicosis (P=.004).
Mizuno et al25 compared the normal (nonrosacea) population with and without Demodex-infested eyelashes and found that the 2 groups were not significantly different for meibomian gland dysfunction, fluorescein TBUT, or ocular surface discomfort.
Varying results have been reported regarding the association between Demodex and blepharitis or ocular surface discomfort with or without rosacea. In our study, we found that Demodex did not affect tear function tests or meibomian gland function in patients with rosacea. We believe this study is important because it demonstrates the effects of Demodex on ocular findings in patients with cutaneous rosacea.
Limitations
Our study has some limitations. The number of patients was relatively small, resulting in few significant differences between the comparison groups. A larger prospective research study is required to assess the prevalence of Demodex mites in the ocular rosacea population along with associated symptoms and findings.
Conclusion
Rosacea is a chronic disease associated with skin and ocular manifestations that range from mild to severe, that progresses in the form of attacks, and that requires long-term follow-up and treatment. Rosacea most often presents as a disease that causes ocular surface inflammation of varying degrees. Demodex infestation may increase cutaneous or ocular inflammation in rosacea. Therefore, every patient diagnosed with rosacea should be given a dermatologic examination to determine Demodex positivity and an ophthalmologic examination to determine ocular manifestations.